{ independency injection }

I created a super-simple extension-method for doing class-based token replacement on strings, using reflection. You can just pass a C# object to this function and it will replace tokens matching the object's property values in a straight-forward, easy way.

One of the best-practices recommendations I have struggled with is to have all your <script> tags at the bottom of the page. This is easily accomplished from a standard view; Create a section in your layout called "scripts" that renders just below where you load the libraries and use this section wherever you need scripting. No problem.

Notice I said, "standard view"? What happens if you have a partial that requires some script to run? Some would argue that the scripts should not be in the partial, but I have had a few special cases where this simply isn't possible.

I have a common "Message" partial, who's job is to render messages to the page. Most of these messages are HTML and display normally, but some messages are actually "growl" type notification messages and the partial needs to execute a function on rendering. HERE is the problem. You can't write to a section from a partial, plus partials are sometimes rendered via AJAX.

I needed a way to get the script block from my partial rendered after the scripts are loaded if part of an entire view, but I want to load the scripts inline, should I render the partial using AJAX (since the libraries will be loaded already at this point).

Sure, I could use a Head.js or some other script loading library, but some of these break the "unobtrusive" libraries that come with MVC and I didn't want to lose that functionality.

Templated Delegates to the Rescue

I created a ScriptBlock extension-method that accepts a templated delegate from anywhere in a view. The extensions method determines if the request is AJAX or not and writes the script back to the view if it is. If the partial is part of an entire view page, the script is captured in a StringBuilder, stored in HttpContext. A counterpart extension method "WriteScriptBlocks" can then be included in my layout, wherever I want the scripts to render.

Check it out.

Extention Methods:

Using the templated delegate as a parameter is great, because any model-view-binding is executed before the content is delivered to this function. Since it's a template, Intellisense and code coloring also works. Here it is, in use:

I have a huge MVC project that I am working with that has a pretty complex routing schema. Debugging routes gets pretty hairy, so I was delighted to find the RouteDebug assembly that Phil Haack put together. It helped me immensely, but my project takes too long to compile for quick route testing.

I needed a quick way of creating routes and testing the route values, so I created a super-light-weight small website to use his assembly with nothing else. You can put your route creation code right into the Global.asax and instantly get the results. I found this super useful and I hope you do too.

You can also use this library to create your own "ActionLink" extensions too. BUT, this isn't why I wrote this article.

I wanted to extend this method to specify an EXACT route to use, as I had a special route to format the URLs and the above method uses the first route it finds that could work - usually the default route.

After struggling for hours trying to parse the expression myself (UGH!), a simple solution presented itself:

There are a million and a half articles out there about Policy Injection and the Policy Injection Blocks (from Enterprise Library). Most of them are by my new favorite blogger, David Hayden. If you aren't familiar with Unity, check out these posts first.

The articles span the life-cycle of Unity from before Policy Injection was introduced and some of the actual type names change from article to article, so it wasn't as straight forward as I am going to make it here.

First of all, I didn't want to use a config file - I wanted to configure my policies in the same place I was configuring my dependencies; in the Global.asax code-behind.

It turns out that this is super easy!

Assuming you already have a reference to the Unity library "Microsoft.Practices.Unity", all you need to add is a reference to the "Microsoft.Unity.Interception" library, found in Microsoft Enterprise Library 4.1.

You probably already have a place where you are configuring your dependencies:

// Register for Dependency Injection

container.RegisterType<IDataContextProvider, DataContextProvider>();

Now all you need to do is setup the container with an extension that's called 'Interception' then configure each of the Interfaces you want to intercept with Policies. Like so:

Now, when you use Unity to resolve your objects, it will detect if any policies are decorated on the interface or the concrete class. If there are policies, Unity creates a transparent proxy object and executes your policies like it does in the Policy Application Blocks. Check out this article to see how to create handlers.

Now you are ready to place your "Policy Attributes" on your classes. Later, I will show you some of my favorite policies I have written for MVC.

In my last article, I showed you a way of creating an interface for the LinqToSql DataContext so that you can mock the actual implementation for unit testing. Well, there is another benifit to creating such an interface. The interface we created, uses LinqToSql's underying generic methods. Using this, we can create a completely generic repository class, to handle all data transactions from our data-layer.

I won't get into the Repository Pattern or Domain Driven Design, because there are too many people out there, WAY smarter than me discussing it in full. I use this pattern mainly for convenience in testing and reducing code, but it is worth reading up on -- it is some great stuff!

First off, there are literally a THOUSAND articles out there talking about the Repository Pattern and quite a few articles discussing implementing this with the LinqToSql DataContext. None of them were quite what I needed, so I present to you, my version with ideas borrowed from this article and this one (both of these concepts are awesome, however they lacked the IDataContext piece so that it can be unit tested.

IDataContext

First, let's assume that you have already followed my last article, and your DataContext implements IDataContext.

This class uses Dependency Injection and accesses the DataContext as IDataContext. This allows us to create unit tests for this class with a mocked data-context.

There are two Get methods, both of which pass a Where expression down to the Linq extensions. The first attempts to build an expression manually. This is assuming that you use int as your IDs. If you don't you can always update the code to fit your needs. GetPrimaryKey() is an extension method written by the genius, Mike Hadlow over here. It's awesome, and I included it down below.

Both return a single instance from the DataContext, but the Get(Expression<Func<T,bool>> selector) function allows a more complex lookup (for complex identities or whatever). It's passed as an expression, just like the "Where()" function, in the Linq extensions.

Sample Usage

So what does this buy us? Well, with this simple generic class we suddenly have a full, strongly-typed repository layer for each object in the DataContext.

// You can now declare and use "specific" repositories for your Linq objects.

_UserRepository = userRepository;

_CarRepository = carRepository;

}

publicvoid DoSomething()

{

// Basic get by ID

var car = _CarRepository.Get(1);

// Complex selector

var differentCar = _CarRepository.Get(c => c.Name == "Ford");

// Basic list

var listOfUsers = _UserRepository.List();

// List, with filters

var filteredUsers = _UserRepository.List()

.Where(u => u.Name.StartsWith("T"));

// Add

_UserRepository.Add(newUser { Name = "Fred"});

_UserRepository.SubmitChanges();

// Update

var editableUser = _UserRepository.Get(1);

editableUser.Name = "New Name";

_UserRepository.SubmitChanges();

}

}

Obviously, you can only create a Repository<T> for a class in your context. Otherwise, you would see an epic exception.

Another great thing about this pattern is it's benifits with code-coverage. You can create unit tests for each of these methods and in effect cover your entire data-layer. Not to mention the value in having less code laying around.

As you know, I have recently become a huge fan of the Dependency Injection (DI) and Inversion of Control (IoC) patterns, but was stumped when trying to implement this pattern down to my data layer. I LOVE LinqToSQL, but I wasn't sure how I could make the Linq DataContext an abstract interface. I stumbled upon a great article discussing How to make the DataContext "Unit Testable". From this, I boiled down a version of an interface that was easy to implement in the DataContext.

An Interface for the DataContext: IDataContext

LinqToSql exposes Sql Server tables as theunmockable Table which is a sealed class. But LinqToSql namespace has an interface ITable which the Table type implements and that is easy to mock, also this ITable exposes InsertOnSubmit, InsertAllOnSubmit, DeleteOnSubmit, DeleteAllOnSubmit. So in our interface we exposed the ITable instead of that concrete Table which makes this partial Database class completely unit testable.

As you can see, all the basic functions of the DataContext exist for your consuming class.

Implement that Sucker

Now we need to implement this interface in our DataContext. Right-click on your DBML file, and select "View Code". This creates a partial class file for the DataContext. In it, you can implement the interface.

Example Usage

Now, your consuming classes are free to use the DataContext as the Interface "IDataContext" which can be mocked in Unit Tests.

publicclassSomeController

{

readonlyIDataContext _DataContext;

public SomeController(IDataContext dataContext)

{

_DataContext = dataContext;

}

publicvoid DoSomething()

{

var foo = _DataContext.GetQueryable<Foo>()

.SingleOrDefault(f => f.FooId == 1);

}

}

Conclusion

This demonstrates how you can make your DataContext an interface that is mockable and could be injected at runtime for DI. In the next article, I will show how you can create a generic repository using the IDataContext.